The present invention relates very generally to liquid dispensing machines such as a beverage dispensing machine. More particularly, the invention pertains to a sensor for detecting an out-of-syrup condition, particularly in association with a dispensing machine that dispenses a liquid comprised of water and a flavored concentrate syrup which is adapted to be mixed with the water. In this regard, reference may be made to copending application Ser. No. 590,992 filed Mar. 19, 1984, now U.S. Pat. No. 4,645,095 which relates to an automatically controlled apparatus for providing for self-fill of the tank of the dispensing machine, particularly such a machine that dispenses a liquid comprised of water and a flavored concentrate syrup.
Presently existing syrup probe sensors have not operated totally effectively and sometimes have provided false readings. This has been due, to a large measure, to the lack of compensation for different types of liquids that are being sensed. For example, highly acidic concentrates are very conductive and therefore have a low resistance. Conversely, highly sugared syrups are poor conductors and have a high resistance. In the past, probes have been fine tuned by the use of a potentiometer to operate within a range of the particular fluid being monitored.
An example of a prior art syrup probe sensor is illustrated herein in FIG. 7. FIG. 7 shows a sensor housing 2 which may be constructed of a plastic non-conducting body and, supported therein, stainless steel fittings 3 and 4. A resistance is measured between the fittings 3 and 4 as illustrated by the electrical polarity signals indicated in FIG. 7. It is noted in FIG. 7 that even when out of syrup, a conductive film 5 remains. Particularly, when the syrup is thick, the film is appreciable and conductive. With the arrangement of FIG. 7, the film was very slow in dissipating or draining away and sometimes remained even after a long period of time. Hence, it was very difficult to obtain a clean shut-off or pick up of the out-of-syrup condition. Even with the use of a variable resistor to try to accommodate various syrups, the operation was still unreliable and unpredictable.
Accordingly, it is an object of the present invention to provide an improved means for sensing syrup or the like concentrate being delivered to a storage tank in which it is mixed with water.
Another object of the present invention is to provide an improved out-of-syrup sensor which is adapted to operate effectively regardless of the type of syrup concentrate that is being used.
Still another object of the present invention is to provide an improved out-of-syrup sensor for use with a dispensing machine that dispenses concentrate beverages and in which the out-of-sensor apparatus operates so as to prevent false indications.
Another object of the present invention is to provide an improved out-of-syrup sensor which is of more simplified construction eliminating the need for external trimming components such as potentiometers.